Well the fact is that there are. In addition to already having the aforementioned tags for signatures for flickr and instagram, there are threads already dedicated to that, if you feel the need to share even more explicitly.
i.e.
Instagram:
viewtopic.php?f=5&t=39405flickr:
viewtopic.php?f=8&t=6402In addition to many others on the subject. The search engine is your friend.